This invention relates to cardiac pacing, and more particularly to the optimization of cardiac output in physiologic dual chamber modes of pacing.
Because of the autonomous nervous system regulation of the atrio-ventricular node, the PR interval is usually decreased as the heart rate increases among subjects having a healthy heart. The problem of rate responsive sequential cardiac pacing (DDDR mode) and the P wave synchronous ventricular pacing (VDD mode) is to maintain this natural heart behavior in the case when the heart block prevents the natural atrio-ventricular delay shortening. Therefore, contemporary cardiac pacemakers, especially dual chamber rate responsive models, comprise the "rate responsive AV delay"programming feature. The advantage of such pacemakers is that, due to the reduction in the overall refractory period, the physical capacity of a patient is increased by enabling greater maximum tracking rate. However, the criteria for the software algorhythm which controls this special pacemaker function timing have not been appropriately solved.
Pacemakers currently available on the market and produced by various manufacturers determine the AV delay timing by means of the mathematical relationship between the AV interval and the heart rate. The linear correlation between PR interval and heart rate during exercise was described in the paper "Physiological Relationship Between AV Interval and Heart Rate in Healthy Subjects: Application to Dual Chamber Pacing", published by C. Daubert and co-workers in PACE 9:1032, 1986, incorporated herein. Despite the fact that various manufacturers use various algorhythms including an exponential as well as a linear relationship between heart rate and atrio-ventricular interval shortening, none of them measure some hemodynamic parameter and as a consequence adjust the A-V interval. There is a theoretical possibility in all pacing systems which measure the cardiac output to adjust the A-V interval in order to achieve the maximum cardiac output. In our earlier patent application U.S. Ser. No. 674,607, filed Mar. 25, 1991,and fully incorporated herein, we disclose an electrotherapy system controlled by means of the tricuspid flow waveform. The same system was described in the European patent applications "Cardiac Electrotherapy System" and "Ultrasonic Doppler Synchronized Cardiac Electrotherapy Device" having serial numbers 91104561.5 and 91104555.7, respectively. This system enables the exact optimization of the A-V interval by means of the monitoring of the ventricular filling pattern and keeping the optimal waveform timing. This application is a continuation-in-part of that earlier application.